The present invention relates in general to the use of x-ray sources in microlithography for integrated circuits.
X-ray lithography of integrated circuit wafers involves the exposure of patterned photoresist on the wafers with a source of radiation to form desired circuit patterns. UV radiation has been used in the past for lithography. However, with the continuing trend toward smaller and smaller circuits, UV radiation is becoming unsuitable because it can not provide the necessary resolution for very small detailed circuit patterns. Researchers have thus begun to look toward other suitable sources of radiation for microlithography. Many experiments have been conducted with soft x-rays as one suitable alternative source. Synchrotron sources, pulsed laser sources and gas-puff z-pinch sources have been under study for this purpose. The synchrotron is very expensive and generates a high intensity, low divergence x-ray beam that provides a very narrow exposure field. This requires that the photoresist on a few centimeter diameter circuit wafer be scanned by the x ray beam to be fully exposed. Laser plasmas and gas-puff z-pinches are capable of producing high intensity pulses of x-rays, but when a wafer is placed far enough away from the source that resist exposure will be adequately uniform, the x-ray fluence on the photoresist is reduced to a point that many pulses are required to expose it. Further, the location of the x-ray emissions in z-pinch x-rays tends to be unpredictable which further tends to make them unsuitable for microlithography.